How to extrude all edges 1cm from center point?
With the loop selected, press AltS to scale it
along the normals.
Press S again to activate Even Thickness, so you define the actual width of the border instead of the corner edges' length.
Enter -.01 to get a border of 1cm width.


The edges don't provide normals to scale along, so the adjacent faces' normals are used, which are pointing inwards. This is why you have to enter a negative distance.